Polymer nucleating agents are often included in thermoplastic crystalline and semi-crystalline polymers. They act as sites or nuclei for initiating polymer crystallization, thereby producing a greater number of smaller crystalline domains or “spherulites” in the solidified product. The result is that that polymer usually has a higher degree of crystallinity, which in turn normally results in an increase in hardness, elastic modulus, tensile strength and yield point compared with untreated polymers. Other properties such as ductility (elongation at break), impact strength and optical properties such as transparency, haze reduction and translucency are also often improved. Crystallization temperatures are often increased by nucleating agents. This leads to shorter cycle times during injection molding and like processes because less cooling is needed to achieve solidification. See Jansen et al., Nucleating Agents for Partly Crystalline Polymers, pp. 862-875, Plastics Additives Handbook, edited by Gachter & Muller, Hanser-Gardner Publications, Inc., Cincinnati, Ohio, © 1993, the disclosure of which is incorporated herein by reference, for a discussion of nucleating agents and their effect on crystalline and semi-crystalline polymers.
Many different materials, both organic and inorganic, are known to function as polymer nucleating agents. See, for example, U.S. Pat. No. 5,300,549 and U.S. Pat. No. 6,465,551. See, also, U.S. Pat. No. 6,537,665, which discloses that certain alumina-coated silica nano-powders carrying a surface coating of an organic acid also function as polymer nucleating agents. Finally, also note U.S. Pat. No. 5,310,950 to Michael J. Mannion, which teaches that certain ultrafine sorbitol and xylitol acetals work exceptionally well as clarifying agents in semi-crystalline polymers. The disclosures of all of these documents are incorporated herein by reference.